The present invention relates to heater control system for a patient warming apparatus and, more particularly, to a system for controlling the heater used on an infant warmer.
In the care of newborn infants, there are various types of apparatus that provide heat to an infant and such apparatus can include infant incubators, infant warmers and combinations of the two. In such apparatus, there is normally provided, an infant platform on which the infant is positioned so as to receive the care and that infant platform is a generally planar surface located so as to underlie the infant.
With an infant incubator, there is normally a heater that is located in a compartment beneath the infant platform and that heater is generally an electrically powered heater that warms air that is then circulated through an infant compartment that encloses the infant resting on the infant platform. An example of an infant incubator is shown and described in U.S. Pat. No. 4,936,824 of Mackin et al.
As to combination apparatus, the apparatus can function as an infant warmer or an infant incubator by the use of a vertically movable canopy supporting a radiant heater to provide radiant energy when the apparatus is functioning as an infant warmer as well as a convective heater system that is utilized when the apparatus is functioning as an incubator. Examples of such combination apparatus are shown and described in U.S. Pat. No. 6,224,539 of Jones et al and U.S. Pat. No. 6,083,020 of Jones et al.
In the case of an infant warmer, there is also normally a radiant heater that is positioned above the infant platform and which includes a resistance heater element that directs that radiant energy, in the infrared spectrum, toward the infant platform so as to provide heat to an infant lying on that infant platform.
An infant warmer is shown and described in U.S. Patent No. 5,474,517 of Falk et al as prior art to that patent and a particular geometry of an infant heater is shown and described in U.S. Pat. No. 6,245,010 of Jones et al.
With such heaters, whether for radiant or convective systems, it is certainly desirable to have as accurate a control of the power to the heater as possible and, to the end, it would be advantageous to have a system that directly measured the power being applied to the heating element of a heater in an infant warming apparatus in order to accurately establish a desired power of the heater to direct a specific and accurate amount of heat to the infant.
A heating control system is disclosed in U.S. Pat. No. 6,271,506 where the current is determined along with the voltage, however, there is no direct determination of the power to the heater element since the line voltage is sensed and not the voltage across the heater element. The system of the '506 patent would not, therefore, provide a direct measurement of the power to the heater element and would suffer from the inaccuracies discussed herein with respect to FIG. 2 of this application.
Accordingly it would be advantageous to have a radiant heater control system that directly measures the power applied to the heater element and then controls the power to heater based upon that measurement.